Friction stir welding (FSW) produces welds using a combination of frictional heating of metal by a rotating tool, and mechanical deformation of the metal by the tool. The tool may include a weld tip comprising a rotating pin surrounded by annular shoulder. FSW tools can be used to perform various types of FSW welding, including fixed tool welding, retractable pin-tool welding and fixed stir spot welding. In order to practice these welding techniques, the pin is designed to retract relative to the shoulder, and both the pin and the shoulder may be independently rotated at the same or different speeds, in the same or opposite directions. The pin penetrates the workpiece and the shoulder rubs top surfaces of the heated metal to produce a weld joint. As the weld is completed, the tool shoulder and pin are withdrawn from the workpiece.
In order to move a FSW weld tip along a desired weld path, the weld tip may be mounted on a weld head that forms part of a multi-axis motion platform similar to a CNC machining center. In the case of workpieces having more complicated, contoured surfaces, such as those sometimes used in aircraft subassemblies, the problem of coordinating the movements of the FSW weld tip along a highly contoured weld path is challenging.
Further complicating the task of FSW process control is the need to provide auxiliary process capabilities such as milling, drilling and probing. For example, light milling of the workpiece is often required in order to remove flash or runoff tabs on the workpiece. Drilling may be required to produce through-holes in the workpiece at mounting locations. Probing may be required in order to locate workpiece features so that the exact position of the features is known in relation to the weld tip.
As a result of the forgoing requirements, CNC-type FSW machines have been produced that are capable of performing multiple FSW operations, including milling, drilling and probing. These processes use different tools and require differing control processes and control parameters. Thus, separate, sometimes proprietary, control systems and software logic may be required to support the individual machine processes, resulting in a relatively complex control system that may lack needed flexibility, particularly when tools or processes must be changed or added to the system.
Accordingly, there is a need for a process control system for FSW machines having a simplified, open architecture that is flexible and readily adaptable to accommodate new or different tools or processes. Embodiments of the disclosure are directed toward satisfying this need.